Asphalt-based roofing materials, such as roofing shingles, roll roofing and built-up roofing, are installed on the roofs of buildings to provide protection from the elements. Typically, the roofing material is constructed of materials including a reinforcing mat such as a glass fiber mat, an asphalt-based coating which saturates the mat and coats the front and back and a layer of surfacing granules adhering to the top coating as well as a backdust material to cover the back coating. The asphalt-based coating usually contains a filler such as pulverized limestone.
The quantity, composition and properties of the raw materials used to make a roofing material determine, to a great extent, the performance of the resultant roofing material (e.g., weathering durability, cracking, blistering, algae resistance, pliability, sticking, and impact resistance). They also determine the cost to produce the roofing material, and its weight. For a roofing shingle, the cost to produce the shingle is usually about 60-80% materials cost.
Traditionally, the roofing material weight has been linked to its quality and durability, perceived as a primary indicator for the amount of asphalt used and for the product performance. However, the product weight can be misleading, since the asphalt contributes to only a small part of the total weight. For a given amount of asphalt in a roofing material, its product weight depends largely on the quantities and densities of other raw materials like filler, granules, and backdust material used, which fill up the volume or cover the surface of the roofing material. These raw materials can be selected from many kinds of mineral or waste materials in different densities, which meet the requirements for the manufacture of quality roofing materials. When the raw material density changes, the roofing material weight will vary, but its performance may not be necessarily impacted. When purchased by weight and used for volume filling or surface covering, the densities of the raw materials can become a leverage for balancing product weight and cost.
In the trend of rising energy costs, an unnecessarily heavier product may result in a higher transportation cost without benefits to the product performance. Moreover, a heavier roofing product increases the labor intensity and risk of ergonomic injuries during handling and application.
One weight-increasing material that typically does not add to the useful properties of the installed shingle is the backdust material. Roofing shingles usually have a backdust material on the bottom coating to prevent them from sticking together in a bundle or from sticking together in a roll. The backdust is typically made from rock, which may be crushed as in talc, carbonate or rock dust. The backdust may also be produced by screening sediment, such as silica sand.
In view of the current roofing materials, there is obviously a need for roofing materials that are optimized as a whole for performance, material and transportation costs and application convenience. There is also a need for a process for making such roofing materials.
The invention will be more readily understood from the following description of a preferred embodiment thereof given, by way of example, with reference to the accompanying drawings.